The present invention relates to a system for inspecting circumferential welded joints in pipe lines etc., using ultrasonic waves. Prior art systems of this type are known. It is during the construction of pipe lines for transporting, for instance, gas and oil extremely important that all the security requirements presented by the authorities are met.
Therefore it is necessary to inspect the welded joints with the utmost reliability. Furthermore such inspection should be carried out fast in order not to delay the pipe laying operations. That applies both to the construction of pipe lines on land and to the construction of pipe lines on the sea bottom. Until now the welded joints between the pipe sections have been examined radiografically. As a result of the rather restricted detection sensitivity of said radio graphic method for two-dimensional defects, for instance cracks or lack of side wall fusion, one has looked for other methods such as magnetic crack detection and for ultrasonic testing. Especially ultrasonic testing has a number of advantages. It is for instance possible to use relatively light weight and handy apparatusses and to inspect materials with greater thickness. Furthermore there is no radiation danger, an increased detection sensitivity for two-dimensional defects, an easier dephth determination of defects, the possibility to mechanize the ultrasonic scanning with related registration, and there is no need to introduce a device into the pipe line. Especially with the mechanized ultrasonic method, the examination time does not necessarily increase with the wall thickness, as is the case when using radiagrafical methods.